A few words on the life of a tree may be welcomed here by those readers who have not made a study of botany. Although the nurseryman makes use of suckers and cuttings for the quicker multiplication of certain species, every tree in its natural habitat produces seeds and is reproduced by them. The flowering of our forest trees is a phenomenon that does not as a rule attract attention, but their fruiting or seed-bearing becomes patent to all who visit the woods in autumn. A tree has lived many years before it is capable of producing seed. The seed-bearing age is different in each species; thus the Oak begins to bear when it is between sixty and seventy years old, the Ash between forty and fifty, the Birch and Sweet Chestnut at twenty-five years. Some produce seed every year after that period is reached, others every second, third, or fifth year; others, again, bear fitfully except at intervals of from six to nine years, when they produce an enormous crop. Most tree-seeds germinate in the spring following their maturity, but they are not all distributed when ripe. The Birch, the Elm, and the Aspen, for examples, retain their seeds until spring, and these germinate soon after they have been dispersed.
The seeds contain sufficient nutriment to feed the seedling whilst it is developing it roots and first real leaves. We can, of course, go further back in starting our observations of the life progress of the monarch of the forest. We can dissect the insignificant greenish flower of the Oak when the future seed (acorn) is but a single cell, a tiny bag filled with protoplasm. From that early stage to the period when the tree is first ripe for conversion into timber we span a century and a half, equal to two good human lives, and the Oak is but at the point where a man attains his majority. The Oak is built up after the fashion by which man attains to his full stature. It is a process of multiplication of weak, minute cells, which become specialized for distinct offices in the economy of the vegetable community we call a tree. Some go to renew and enlarge the roots, others
to the perfecting of that system of vessels through which the crude fluids from the roots are carried up to the topmost leaf, whence, after undergoing chemical transformation in the leaf laboratory, it is circulated to all parts of the organism to make possible the production of more cells. Each of these has a special task, and it becomes invested with cork or wood to enable it to become part of the bark or the timber; or it remains soft and develops the green colouring matter, which enables it, when exposed to sunlight, to manufacture starch from carbon and water.
This is very similar to what takes place in the human organism, where the nutriment taken in is used up in the production of new cells, which are differentiated into muscle-cells, bone-cells, epidermal-cells, and so forth, building up or renewing muscles or nerves, bones or arteries; but the mechanism of distribution is different, the heart-pump doing the work of capillary attraction and gravitation. The ancients believed in the Dryads, spirits that were imprisoned in trees, and whose life was coterminous with that of the tree; and it will be seen that they had stronger physical justification for their belief than they knew. Shakespeare relates how Sycorax, the witch-mother of Caliban, imprisoned Ariel in a tree; and Huxley finely tells us that "The plant is an animal confined in a wooden case; and Nature, like Sycorax, holds thousands of 'delicate Ariels' imprisoned in every oak. She is jealous of letting us know this; and among the higher and more conspicuous forms of plants reveals it only by such obscure manifestations as the shrinking of the Sensitive Plant, the sudden clasp of the Dionæa, or, still more slightly, by the phenomena of the cyclosis."
The tree, as we have indicated, gets its food from the air and the soil. The rootlets have the power of dissolving the mineral salts in the soil in which they ramify; some authorities believing that they are materially helped in this respect—so far as organic matter is concerned—by a fungus that invests them with a
mantle of delicate threads. However that may be, the fluid that is taken up by the roots is not merely water, but water plus dissolved mineral matter and nitrogen. At the same time as the roots are thus absorbing liquid nutriment, the leaves, pierced with thousands of little stomata, or mouths, take in atmospheric air, which is compounded chiefly of the gases oxygen and carbon. The leaf-cells containing the green colouring matter (chlorophyll) seize hold of the carbon and release the oxygen. The carbon is then combined with the fluid from the roots by the vital chemistry of the leaves, and is circulated all over the system for the sustenance of all the organs and tissues.
The flowering of the trees varies so greatly that it can only be dealt with satisfactorily as each species is described. It may be stated, however, that all the true forest trees are wind-fertilized, and therefore have inconspicuous greenish blossoms. By true forest trees we mean those that alone or slightly mixed are capable of forming high forest. The smaller trees, such as Crab, Rowan, Cherry, Blackthorn, Hawthorn, Buckthorn, etc., belong more to the open woodland, to the common and the hedgerow. These, from their habitat, can be seen singly, and therefore can make use of the conspicuous flowers that are fertilized by insects.